Cable interface for a wind power facility

ABSTRACT

A cable interface system ( 20 ) for connecting internal cabling of a wind power facility ( 10 ), the cable interface system ( 20 ) comprising: a tower interface ( 32 ) associated with a tower ( 14 ) of the wind power facility ( 10 ), the tower interface comprising a support structure ( 80, 90 ) that is arranged to support a set of tower cables ( 36 ) in a fixed configuration; a nacelle interface ( 30 ) associated with a nacelle ( 18 ) of the wind power facility ( 10 ), the nacelle interface comprising a support structure ( 40 ) that is arranged to support a set of nacelle cables ( 34 ) in a fixed configuration; wherein the tower interface ( 32 ) is dockable with the nacelle interface ( 30 ) so that each tower cable ( 36 ) generally aligns with and can be joined to a corresponding nacelle cable ( 34 ).

TECHNICAL FIELD

The invention relates to a cable interface for a wind power facility, inparticular, but not exclusively, to an interface for aiding installationof internal cables of such a facility.

BACKGROUND TO THE INVENTION

Wind power facilities including a wind turbine mounted on top of asupport structure such as a tower typically include internal cablingthat runs from a nacelle of the turbine to the bottom of the tower andbeyond. The cabling may include, for example, power transmission linesto deliver electrical power produced by the turbine generator to anexternal power grid, internal power cables for powering auxiliarysystems, and data cables carrying control data and/or measurement databetween the nacelle and remote systems, for example a SCADA (supervisorycontrol and data acquisition) system.

Large wind power facilities cannot be transported to a site in anassembled state, and so must be erected at the site. This entailsinstalling and connecting the internal cabling at the site, which isdifficult, time-consuming, and potentially hazardous; particularly inthe case of offshore wind power facilities. There is therefore a desireto ease the process of cable installation to reduce the time required toperform this task.

It is known to use a rigid curved steel tube, or ‘J-tube’, disposedwithin the tower of the wind power facility to act as a guide andsupport for a transmission line that is drawn up through the J-tubeuntil reaching a transition piece that ultimately supports the line.Electrical connections to the line can then be made as required. TheJ-tube ensures that bending of the transmission line is controlled,thereby preventing damage to the line during and after installation.EP2696123 discloses a development on this theme, in which a flexiblereinforced protective tube is used to protect the transmission line, theline and the protective tube being lifted together to the transitionpiece.

While such arrangements ease moving the transmission line into position,they do not help with the complicated task of making electricalconnections to components of the wind turbine. Wind power facilities mayhave one or more cable bundles, each potentially containing dozens ofindividual cables. For example, bulky high voltage power transmissioncables are often divided into bundles of multiple cables to improveflexibility. Connecting each of these cables within the nacellerepresents a considerable burden on the installer.

It is against this background that the invention has been devised.

SUMMARY OF THE INVENTION

In a first aspect, the embodiments of the invention provide a cableinterface system for connecting internal cabling of a wind powerfacility, the cable interface system comprising:

-   -   a tower interface associated with a tower of the wind power        facility, the tower interface comprising a support structure        that is arranged to support a set of tower cables in a fixed        configuration;    -   a nacelle interface associated with a nacelle of the wind power        facility, the nacelle interface comprising a support structure        that is arranged to support a set of nacelle cables in a fixed        configuration;    -   wherein the support structure of the nacelle interface comprises        a respective terminal for each nacelle cable, each terminal        being arranged to receive an end of a respective nacelle cable,    -   wherein the tower interface is dockable with the nacelle        interface so that each tower cable generally aligns with and can        be joined to a corresponding nacelle cable.

Advantageously, the invention provides a nacelle unit that isself-contained in the sense that power transmission cables are alreadyconnected to the power generation components that are located in thenacelle. The interface system can be assembled offsite, and then thenacelle interface and the tower interface can be brought together duringerection of the wind turbine so as to complete the electricalconnections. This makes the assembly process of the wind turbine moretime efficient since it removes the task of making the cable connectionsfrom the ‘critical path’ of the assembly process.

The support structure of the nacelle interface may include a terminalfor each nacelle cable, each terminal being arranged to receive an endof a respective nacelle cable.

In an embodiment of the invention each terminal is selected from a groupof compression or mechanical connectors.

The high voltage DC cables require a secure and permanent connector tofunction reliably. This is achieved with a compression or mechanicalconnector.

In the context of the present application the term “terminal” or“connector” uses the definition of the International ElectrotechnicalCommission (IEC) IEV ref. 461-17-03: “metallic device to connect cableconductors together”.

To the skilled person the term “compression connector” is known to be aconnector type that uses the technique of “compression jointing” toestablish a permanent connection between conductors. “Compressionjointing” is defined in International Standard IEC 61238-1 as a “methodof securing a connector to a conductor by using a special tool toproduce permanent deformation of the connector and the conductor.

To the skilled person the term “mechanical connector” is known to be aconnector type that uses the technique of “mechanical jointing” toestablish a permanent connection between conductors. “Compressionjointing” is defined in International Standard IEC 61238-1 as a “methodof securing a connector to a conductor, for example by means of a boltor screw acting on the latter by alternative methods”.

Compression and mechanical connectors are commercially availableconnector types used to establish a permanent connection between twoconductors, i.e. between the conductors of the nacelle cables and thetower cables.

In order that the tower interface may be brought towards the nacelleinterface, the nacelle interface may include a winch. The winch mayconnect to a coupling on the tower interface so that the tower interfacecan be raised for docking with the nacelle interface.

In one embodiment the support structure of the tower interface includesa set of apertures, each of which receives one of the tower cables, theapertures serving to keep the cables in proper alignment and in a spacedconfiguration. Each aperture may include a lock arranged to secure therespective one or more tower cables within the aperture such that an endof the or each tower cable is exposed for connection to a correspondingnacelle cable.

In one embodiment, the nacelle interface and the tower interface mayinclude complementary docking formations arranged to engage with eachother for docking of the tower interface with the nacelle interface.Beneficially, the docking formations may include a lock that preventsdisengagement of the docking formations. Personnel can therefore work onthe cables at and below the tower interface whilst the lock is in placebut before full connection between the docking formations has beencompleted.

In another aspect the invention resides in a nacelle interface thatprovides one or more external connection points for one or morecorresponding nacelle cables residing within a nacelle of a wind powerfacility, the connection points enabling each nacelle cable to beconnected to a respective cable supported below the nacelle, the nacelleinterface comprising a support structure that is arranged to support thenacelle cables in a fixed configuration.

In a further aspect, the invention resides in a tower interface arrangedto support a set of tower cables within a tower of a wind powerfacility, the tower interface comprising a support structure that isarranged to support the set of tower cables in a fixed configuration,the tower interface being arranged to dock with the nacelle interface(of claim 12 so that each tower cable aligns with a correspondingnacelle cable.

BRIEF DESCRIPTION OF THE DRAWINGS

So that it may be more fully understood, the invention will now bedescribed, by way of example only, with reference to the followingdrawings, in which:

FIG. 1 is a perspective view of a portion of a tower-mounted windturbine including a cable interface according to an embodiment of theinvention;

FIG. 2 is a front perspective view of a cable interface according to anembodiment of the invention;

FIG. 3 is a rear perspective view of the cable interface shown in FIG.2;

FIG. 4 corresponds to FIG. 3 but shows a detail view of a nacelleinterface of the cable interface;

FIG. 5 corresponds to FIG. 3 but shows a detail view of a towerinterface of the cable interface;

FIG. 6 corresponds to FIG. 5 but shows a detail view of a portion of thetower interface;

FIG. 7 corresponds to FIG. 1 but shows the tower-mounted wind turbinefrom below; and

FIG. 8 corresponds to FIG. 1 but shows a detail view of the cableinterface.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring firstly to FIG. 1, an upper portion of a wind power facility10 is shown. The wind power facility (10) includes a wind turbine 12mounted on top of a tower 14, the wind turbine 12 being composed of arotor 16 supported by a nacelle 18. The nacelle 18 houses a generatorarranged to convert kinetic energy of the rotor 16 into electricalenergy, as well as various auxiliary systems providing cooling, controland monitoring, for example.

To aid understanding of the internal structure of the wind powerfacility 10, FIG. 1 shows the tower 14 as transparent to reveal internalfeatures such as platforms. It should be appreciated that in reality thetower 14 is a tubular structure that encases these internal features,which as a result are not externally visible. Similarly, the bladesdepicted in this figure are incomplete in that only some internalstructure of the blades is visible, whereas the outer aerodynamic shellsof the blades have been omitted. It is also worth noting the relativelysmall scale of FIG. 1; towers 14 of modern utility scale wind powerfacilities are known to have diameters in excess of five meters,allowing internal space for personnel.

As noted above, various internal cables run between the nacelle 18 andthe bottom (not visible in FIG. 1) of the tower 14, delivering power anddata to external terminals. FIG. 1 shows a cable interface 20 accordingto an embodiment of the invention that facilitates installation of thiscabling. The cable interface 20 is shown in more detail in FIGS. 2 to 8,but is referred to here to indicate its context within the wind powerfacility 10.

Two disc-like vertically spaced horizontal platforms 22, 24 are shown inFIG. 1, between them forming a cable hang-off structure 26 similar tothose already known in the art. Access to and between the platforms 22,24 at various locations, both at the perimeters of the platforms 22, 24and the centres, is provided by way of ladders 28, to ensure thatpersonnel can access the cables for installation.

As the wind power facility 10 is assembled on site, rather than duringmanufacture, the internal cabling cannot be completely installed priorto transporting the facility 10 to the site. In this embodiment, tominimise the installation effort required at the site, bulky bundles ofpower transmission cables (which may be ‘low’ or ‘high’ voltage) areprovided in two sections: a nacelle portion that resides inside thenacelle 18, and a tower portion that connects to its respective nacelleportion and extends down the length of the tower 14 and beyond. Lightercables such as those for data transmission or low-voltage internal powercables are easier to handle for installation and so are not divided intoportions.

The nacelle portions of the cables are connected to the output of arectifier attached to the wind turbine generator, to transmit DCelectrical power, via the tower portions once connected, to an inverterat the bottom of the tower 14. The inverter produces an AC supply for anexternal power grid, and it should be noted that the inverter is notshown in FIG. 1 since the tower bottom is not shown in FIG. 1; only anupper portion of the tower is shown. The free ends of the nacelleportions are gathered into a bundle by the cable interface 20, forsubsequent connection to their respective tower portions. It is notedthat the generator equipment and the external connections are notvisible in the figures, and are described here to provide context.

This arrangement provides a self-contained nacelle unit that can beassembled off-site, in which power transmission cables are alreadyconnected to the nacelle rectifier. This removes the task of makingthose connections from the ‘critical path’, namely the series of tasksthat cannot be completed in parallel and so define the overall assemblyperiod.

Once the wind power facility 10 has been assembled, the tower portionsare drawn up the tower 14 for connection with their correspondingnacelle portions. The cable interface 20 minimises the burden ofconnecting the portions of the power transmission cables in situ byorienting each of the nacelle portions and tower portions so that theylocate opposite one another once they reach the hang-off structure 26,ready for quick connection, as shall become clear in the descriptionthat follows.

For now, it is observed that the cable interface 20, once installed, issuspended from a lower surface of the nacelle 18 to hang above theuppermost platform 24 of the hang-off structure 26. This arrangementlocates the connection points between the cable portions generally ateye-level for a person standing on the uppermost platform 24, whicheases installation.

Moving on now to FIGS. 2 and 3, the cable interface 20 is shown inisolation in disassembled state, making clear that that cable interface20 is composed of two distinct sub-assemblies: a nacelle interface 30,shown uppermost in FIGS. 2 and 3; and a tower interface 32. Theseinterfaces are configured for inter-engagement so as to hold nacelleportions 34 and tower portions 36 respectively of the facility cablessecurely in position during final installation.

In this embodiment, the nacelle interface 30 forms part of the nacelle18 and is assembled with the nacelle portions 34 before the wind turbine12 is transported to the installation site for mounting onto the tower14. The nacelle interface 30 holds the nacelle portions 34 in apre-determined configuration. The tower interface 32 is used to supportbundles of the tower portions 36 in a configuration that complementsthat of the nacelle portions 34, so that when the nacelle interface 30and the tower interface 32 are brought together, corresponding pairs ofnacelle portions 34 and tower portions 36 face each other in alignmentand so can be connected quickly and easily.

The nacelle interface 30 is shown in isolation in FIG. 4, and has asupport structure 40 including means for guiding and supporting a rangeof cables about its circumference. The support structure 40 comprises atubular engagement portion 42 extending away from and orthogonal to thecentre of a lower face of a bulkhead 44, the engagement portion 42terminating in an end face 46 to define an internal cavity 48. In thisembodiment, the bulkhead 44 is shown as having a cuboid form, forillustrative purposes only.

The end face 46 has a circular central opening 47 which is surrounded bya ring of smaller holes (not shown) that receive bolts for attachment ofthe tower interface 32. The central opening 47 is arranged to receive anose 50 of the tower interface 32, which is shown in FIG. 5 and isdescribed later, the nose 50 acting as a guide to locate the towerinterface 32 with the engagement portion 42.

As depicted in FIG. 7, the bulkhead 44 secures to the underside of thenacelle, shown here as a lower surface 52, to cover an opening in thatsurface 52. Returning to FIGS. 2 and 3, the bulkhead 44 comprisesseveral openings 54 that permit the bundles of nacelle portions 34 ofthe power transmission cables of the wind power facility 10 to exit thenacelle 18 for connection to corresponding tower portions 36. Furtheropenings 54 are included to allow other, undivided cables 56, such asinternal low voltage power cables and fibre optic data cables, to be fedinto the nacelle 18. As noted earlier, these lighter cables 56 are fewerin number and easier to handle than the high voltage power transmissioncables, and so can be connected up inside the nacelle 18 relativelyquickly on site. However, optionally all internal cables can be providedin two portions and installed in the same manner as the high voltagepower transmission cables.

FIG. 4 shows an array of cylindrical pips 58 protruding from the uppersurface of the bulkhead 44. These pips 58 act as spacers between thebulkhead 44 and the nacelle 18 for enabling increased strain in thesecuring bolts for robust assembly.

Below the bulkhead 44, the bundles separate out into individual nacelleportions 34. Multiple arrays of connection points in the form of fixedterminals or connectors 60 are disposed around the engagement portion42, one connector array for each bundle of cables. Each connector arrayis supported by a respective pair of clamp assemblies 62, with one clampassembly 62 securing upper ends of the connectors 60, and the otherclamp assembly 62 of the pair securing lower ends of the connectors 60.This defines an open block-like structure, such that each connectorarray can be considered a connector block 64 for a plurality of cables.Each individual nacelle portion 34 couples to a respective connector 60of a connector block 64, for example by crimping, to create arrays ofconnection points to which respective tower portions 36 can connect.

The engagement portion 42 has two aligned openings formed in its side;the first opening 66 being generally oblong/oval and considerably largerthan the second opening 68, which is semi-circular. The first opening 66provides access to a winch 70 that resides within the cavity 48 of theengagement portion 42, suspended from the underside of the bulkhead 44.The winch 70 is operable to let out a chain 72 to lower a hook 74through the central opening 47 of the end face 46 to couple to an eyebolt 76 of the tower interface 32, and then to recover the chain 72 toraise the tower interface 32 for engagement with the nacelle interface30, as will be explained in more detail later.

The second opening 68 is smaller than the first, and provides an accesspoint for a safety pin 78 whose function is to secure the towerinterface 32 to the nacelle interface 30 temporarily while permanentfixings are made. This temporary coupling shall be described in moredetail later, but it is noted here that the ability to couple the twointerfaces 30, 32 quickly is a benefit as it enables personnel to workbeneath the tower interface 32 to install the permanent fixings; due tohealth and safety regulations, personnel cannot work below a suspendedload until it is secured in place with a mechanical fixing. Therefore,without the temporary fixing, personnel would be restricted to workingfrom above the tower interface 32 to make the permanent coupling, whichwould be a hindrance that would increase the time required for thisoperation.

The tower interface 32 is shown in isolation in FIGS. 5 and 6, in whichit can be seen that the tower interface 32 comprises a cylindrical mainbody 80 surmounted by a disc-like upper flange 82 extending radially tooverhang the upper end of the main body 80 as a skirt. The overhang ofthe upper flange 82 includes a ring of equi-spaced holes 84 thatcorrespond to the ring of smaller holes on the end face 46 of theengagement portion 42 of the nacelle interface 30. Beneath each hole 84is a bolt collar 86 through which bolts can be inserted to secure theupper flange 82 to the engagement portion 42, thereby providing apermanent coupling between the tower interface 32 and the nacelleinterface 30. The bolt collars 86 act to extend both the grippingsurface for bolt heads, and the length of the coupling, therebyincreasing strain in the bolts to provide a more robust coupling.

The nose 50 projects axially from the upper face of the upper flange 82,as viewed in FIG. 5. As noted above, the nose 50 is arranged forinsertion through the central opening 47 of the end face 46 of thenacelle interface engagement portion 42, and into the cavity 48, to actas a guide and to provide a means by which the temporary coupling can beestablished. For this latter function, the nose 50 has a radialthrough-hole 88 for receiving the safety pin 78 of the nacelle interface30. Accordingly, the through-hole 88 is spaced axially from the upperflange 82 to an extent that ensures that the through-hole 88 locatesinside the cavity 48 of the engagement portion 42 of the nacelleinterface 30 to allow access for the safety pin 78 to create thetemporary coupling. Once the safety pin 78 is inserted into thethrough-hole 88, the safety pin 78 prevents withdrawal of the nose 50from the cavity 48 and so provides a temporary coupling.

The eye bolt 76 is mounted on an upper face of the nose 50, the eye bolt76 being used as an attachment point for the hook 74 of the winch 70 ofthe nacelle interface 30, to enable the winch 70 to lift the towerinterface 32 for engagement with the nacelle interface 30.

A cable support 90 in the form of a second, larger flange is disposed atthe lower end of the main body 80 of the tower interface 32, parallel tothe upper flange 82. A series of support flanges 92 dispersedcircumferentially around the main body 80 extend radially from the mainbody 80 and orthogonally to the cable support 90, to brace thestructure.

The cable support 90 includes a series of apertures 94 spaced around itscircumference, each aperture 94 being arranged to receive a cable orbundle of cables. To the front of the cable support 90, as viewed inFIG. 5, are three apertures 94 that receive two low voltage power cablesand one fibre optic data cable. Each cable is held in place by a cablecollar 96 that is a push-fit into the respective aperture 94. It shouldbe noted that although these cables/bundles are shown as solid in theFigure, in reality the visible outer surface of the cable may be simplya light-weight flexible housing or conduit through which relativelylight-weight cables extend.

Four bundles of high-voltage power transmission cable tower portions 36are secured in respective apertures 94 around the rear of the cablesupport 90 as viewed in FIG. 5. Since the bundles are bulkier andheavier than the internal power and data cables, each bundle is securedby both a cable clamp 98 and a cable ‘sock’ 100. As shown more clearlyin FIG. 6, the cable clamp 98 attaches by four bolts to the underside ofthe cable support 90 and clamps onto the cable bundle. The cable clamp98 therefore acts as a lock to hold the bundle in place within theaperture 94. The cable sock 100, which is visible in the lower portionof FIG. 5, is a flexible sleeve, for example made from a metallic mesh,that envelops the cable and which tightens and thus grips the cableunder the tension arising from self-weight of the cable. Each cable sock100 is suspended between a pair of arms 102 that hang from the undersideof the cable support 90 from fixing points 104 disposed to either sideof the respective aperture 94, each fixing point 104 being secured by abolt. The cable socks 100 therefore cooperate with the cable clamps 98to provide additional support for the bundles.

Each bundle separates out into individual cables above the cable support90. As shown more clearly in FIG. 6, a sleeve 106 is provided at thepoint where each bundle separates to ensure integrity of the junction.Free upper ends 108 of the individual cables are exposed to bare metal,to enable secure and reliable electrical connections to be made at theconnection points of the nacelle interface 30. Optionally the free ends108 may be swaged or crimped with ferrule connectors.

As FIG. 6 shows, a shield assembly 110 guards the cable support 90 whereit rests just above the floor level of the upper platform 24 of thehang-off structure 26, for example to protect the cable support 90 fromthe feet of personnel.

FIGS. 7 and 8 provide further context for the cable interface 20 in itsoperating position within the wind power facility 10. As shown in FIG.7, once the tower interface 32 has been drawn up to engage with thenacelle interface 30, and the cable connections made, guards 112 areplaced over the top of the clamp assemblies 62 that support theconnection blocks 64 to protect the connection points thereafter.

In summary, the above described cable interface 20 eases installation ofhigh voltage power transmission cables within a wind power facility 10firstly by dividing those cables into two portions 34, 36, to enableconnections inside the nacelle 18 to be made prior to assembling thefacility 10 on site, and secondly by supporting those cable portions 34,36 in pre-determined configurations, in alignment, and docking the cableportions 34, 36 in those configurations adjacent to each other. Theprocess of connecting the cable portions 34, 36 together is thereforemuch more straightforward than prior art approaches for installinginternal cables. This minimises the assembly operations required onsite, which is an advantage as such operations are more challenging tocomplete on site than in a manufacturing facility.

The skilled person will appreciate that modifications may be made to thespecific embodiments described above without departing from theinventive concept as defined by the claims. For example, the connectorblocks 64 that are described above as mounted to the nacelle interface30 could instead be placed on the tower interface 32, in which case thenacelle interface 30 might include a flange with apertures through whichcables can dangle for connection to the terminals of the tower interface32. Such an arrangement therefore mirrors that of the embodiment shownin the figures and described above.

1. A cable interface system for connecting internal cabling of a windpower facility, the cable interface system comprising: a tower interfaceassociated with a tower of the wind power facility, the tower interfacecomprising a support structure that is arranged to support a set oftower cables in a fixed configuration; a nacelle interface associatedwith a nacelle of the wind power facility, the nacelle interfacecomprising a support structure that is arranged to support a set ofnacelle cables in a fixed configuration; wherein the support structureof the nacelle interface comprises a respective terminal for eachnacelle cable, each terminal being arranged to receive an end of arespective nacelle cable, wherein the tower interface is dockable withthe nacelle interface so that each tower cable generally aligns with andcan be joined to a corresponding nacelle cable.
 2. The cable interfacesystem of claim 1, wherein each terminal is selected from a group ofcompression or mechanical connectors.
 3. The cable interface system ofany claim 1, comprising a winch.
 4. The cable interface system of claim3, wherein the winch is integral with the nacelle interface.
 5. Thecable interface system of claim 1, wherein the tower interface comprisesa coupling arranged to couple to a winch so that the winch can raise thetower interface to dock with the nacelle interface.
 6. The cableinterface system of claim 1, wherein the support structure of the towerinterface comprises a set of apertures, each aperture being arranged toreceive a respective one or more tower cables of the set.
 7. The cableinterface system of claim 6, wherein each aperture comprises a lockarranged to secure the respective one or more tower cables within theaperture such that an end of the or each tower cable is exposed forconnection to a corresponding nacelle cable.
 8. The cable interfacesystem of claim 7, wherein the exposed ends of the tower cables arecrimped or swaged.
 9. The cable interface system of claim 1, wherein thenacelle interface and the tower interface comprise complementary dockingformations arranged to engage with each other for docking of the towerinterface with the nacelle interface.
 10. The cable interface system ofclaim 9, comprising a docking formation lock that is arranged to preventdisengagement of the docking formations.
 11. The cable interface systemof claim 1, wherein the support structure of the nacelle interfaceand/or the tower interface is arranged to support cables that areundivided between the tower and the nacelle of the wind power facility.12. A nacelle interface that provides one or more external connectionpoints for one or more corresponding nacelle cables residing within anacelle of a wind power facility, the connection points enabling eachnacelle cable to be connected to a respective cable supported below thenacelle, the nacelle interface comprising a support structure that isarranged to support the nacelle cables in a fixed configuration.
 13. Anacelle of a wind power facility, the nacelle comprising the nacelleinterface of claim
 12. 14. A tower interface arranged to support a setof tower cables within a tower of a wind power facility, the towerinterface comprising a support structure that is arranged to support theset of tower cables in a fixed configuration, the tower interface beingarranged to dock with the nacelle interface of claim 12 so that eachtower cable aligns with a corresponding nacelle cable.
 15. A method ofproviding electrical connections between a nacelle of a wind powerfacility and one or more terminals external to the wind power facility,the method comprising: connecting a set of nacelle cables inside thenacelle to a corresponding set of external connection points on anacelle interface; raising a tower interface up a tower of the windpower facility, the tower interface supporting a set of tower cablesconnected to the external terminal in a configuration corresponding tothat of the connection points; docking the tower interface with thenacelle interface such that each tower cable aligns with a connectionpoint of a corresponding nacelle cable; and connecting each tower cableto its respective connection point.